A wireless network is a collection of wireless transceivers that communicate over a shared wireless resource in a specified geographic region. Examples are cellular phone networks, wireless local area networks (LANs) and personal area networks (PANs). In the most common networks, a wired base station communicates directly with all the other wireless nodes in the network, without any relaying or cooperation among the nodes. Some wireless networks, however, may use multi-hop relaying in which stationary relay nodes assist mobile nodes by receiving and then retransmitting signals between the base and the mobile nodes. In conventional multi-hop relaying the signal follows a unique linear path through a sequence of one or more intermediate relays, e.g., US 2007/021757. Cooperative relaying, in contrast, takes advantage of spatial diversity by transmitting a signal simultaneously through multiple relays, so the signal takes multiple parallel paths between the source and destination nodes. The destination node receives signals forwarded from multiple relay nodes and combines them with each other (and perhaps also with the direct signal from the source). Typically, the relay nodes in cooperative relaying may also serve as endpoints, so each node acts as both an endpoint for its own communications and a relay for communications of other nodes. Thus, the nodes in the network are cooperating with each other by relaying each other's communications.
It is theoretically expected that cooperative relaying generally should provide some enhanced energy efficiency to wireless networks. However, most cooperative relaying techniques have focused on cellular networks, and specific techniques that provide optimal systems have yet to be fully developed and realized. Cooperative relaying has been combined with specific types of multiplexing techniques such as OFDM. In US 2007/0086512, for example, techniques are presented for assigning different relaying schemes (amplify and forward relaying, decode and forward relaying, and direct transmission without relaying) to different OFDM subchannels to enhance performance. The use of MIMO in such as system is dismissed because it requires a plurality of antennas, increasing hardware complexity and cost. It is also significant to note that the described technique for selecting relaying schemes is not a resource allocation technique for assigning subchannels to specific nodes but rather a technique for assigning a relaying scheme to each subchannel. US 2006/120477 proposes cooperative MIMO communication across base stations, i.e. infrastructure devices, but does not envision mobile client cooperative relaying or resource allocation techniques to conserve mobile device energy. Similarly, US 2005/014193 discusses MIMO relaying techniques with emphasis on infrastructure-based relay stations, but focuses on range extension through MIMO relays. Prior research has also focused on cellular networks.
The increasing demand for higher performance wireless communications, presses existing techniques to their limits. Accordingly, there is a need for new techniques that improve the performance of dense wireless networks and provide other advantages.